A variety of studies of clinical disorders of male reproduction are in progress. Currently we report 1) new information for the interpretation of semen analysis; 2) the first demonstration of an anatomical disorder of the Sertoli cell within the testis of infertile men; 3) evidence for sperm-leukocyte interaction; and 4) demonstration that induction of spermatogenesis in hypogonadotropic men can be accomplished with only 10% of the formerly recommended dosage of FSH. BIBLIOGRAPHIC REFERENCES: Levis, W.R., Whalen, J.J., and Sherins, R.J. Mixed Sperm-Leukocyte Cultures as a Measure of Histocompatibility in Man. Science 191: 302-304, 1976. Sherins, R.J. and Hodgen, G.D., Testicular Gamma-Glutamyl Transpeptidase: An Index of Sertoli Cell Function in Man. J. Reprod. Fertil., 48: 191-193, 1976.